1. Field of the Invention
This invention relates to the field of chemistry and more particularly to novel stable concentrated free-flowing aqueous dispersion compositions containing one or more colorless dyestuff precursors useful in the manufacture of paper for pressure sensitive carbonless duplicating and thermal marking systems; to a process for preparing said dispersions and to the incorporation of colorless dyestuff precursors into pressure sensitive carbonless duplicating manifold systems and thermal marking systems by introducing a concentrated dispersion composition of this invention into coating compositions used in said systems.
2. Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as colorless precursors for carbonless duplicating systems. Among the more important classes, there may be named phenothiazines, for example, benzoyl leuco methylene blue; phthalides, for example, crystal violet lactone; flouorans, for example, 2'-anilino-6'-diethylaminofluoran and 2'-dibenzylamino-6'-diethylaminofluoran; and various other types of colorless precursors currently employed in commercially accepted carbonless copy systems. Typical of the many such systems taught in the prior art are those described in U.S. Pat. Nos. 712,507, 2,800,457 and 3,041,289 which issued July 5, 1955, July 23, 1957 and June 26, 1962, respectively.
These patents and numerous additional patents in the art teach systems in which the colorless precursor is dissolved in a specialized and expensive solvent and then microencapsulated. The microcapsules containing the solutions of the colorless precursors are then coated onto paper out of an aqueous suspension optionally containing a binder. More recently the microcapsules are dispersed in hot wax mixtures and coated on the paper while in the molten state. Typical of the many such systems are those taught in U.S. Pat. Nos. 4,112,138, 4,139,218 and 4,143,890 which issued Sept. 5, 1978, Feb. 13, 1979 and Mar. 13, 1979, respectively. This microencapsulated type of carbonless copy system has several disadvantages. One disadvantage resides in need for specialized and expensive solvents in order to produce the desired solubility of the colorless precursors. The solubility is critical in order to obtain microencapsulated solutions of sufficient concentration for use in pressure-sensitive copying systems. Still another disadvantage is the need to microencapsulate the colorless precursor, which represents a costly additional operation in the manufacture of pressure-sensitive copy and thermal papers.
The following items to date appear to constitute the most relevant prior art with regard to the instant invention.
U.S. Pat. No. 4,138,508, issued Feb. 6, 1979, discloses and claims a paper coating composition comprising a colorless precursor selected from the group consisting of lactone phthalides and lactone fluorans and mixtures thereof dissolved in a carrier oil. The resultant solution is dispersed in a liquid, radiation-curable substance to form a coating composition.
U.S. Pat. No. 3,539,375, issued Nov. 10, 1970, discloses a paper coating slurry comprising water, polyvinyl alcohol, crystal violet lactone, and 4,4'-isopropylidine diphenol for the preparation of thermo-responsive recording paper.
U.S. Pat. No. 3,894,168, issued July 8, 1975, discloses and claims a paper coating slurry comprising water, binder material, and minute water-insoluble, chemically neutral, paper coating particles of mineral, having adsorbed thereon a water-insoluble, chromogenic, substantially colorless basic dye-precursor, the particles being chemically inert to the dye precursor.
Canadian Pat. No. 993,656, issued July 27, 1976, discloses and claims a pressure sensitive carbonless duplicating copy set comprising at least two sheets, of which the top sheet is coated on the under side with a wax containing an acidic developer, and the second sheet coated on the top side with a dyestuff precursor capable of developing a color when brought into intimate contact with the acidic developer.